The present invention relates to an arc chute in a circuit breaker, such as a low-voltage air circuit breaker, for interrupting a relatively large current. In particular, it relates to an improvement for the structure of side members for retaining a plurality of spaced apart arc plates in the arc chute.
In this kind of the conventional circuit breaker such as a circuit breaker disclosed in U.S. Pat. No. 3,296,402, an arc chute comprises a plurality of arc plates of a magnetic material spaced apart from one another, and a pair of side plates of an insulating material for retaining the arc plates on both sides thereof. The arc plates are secured to the side plates by bolts and nuts using upper and lower insulating plates such that the arc plates are spaced from each other with a predetermined separation therebetween.
In such an arc chute, the arc plates are disposed to oppose a switching track of stationary and movable contacts, and arcs generated by the opening operation between the stationary and movable contacts are drawn to the arc plates by an electromagnetic action caused by the arc plates. The arcs are then segmented, cooled, and extinguished by the arc plates. However, since the temperatures of the arcs are high, the arcs heat the atmosphere therearound and generate hot gas. The hot gas is discharged to the exterior of the arc chute through the space between the arc plates. Therefore, side plate portions near the arcs are damaged by the heat of the hot gas, and the dielectric breakdown of the side plates is thereby caused, worsening the performance of the arc chute. The dielectric breakdown due to the heat damage is especially severe in portions of the side plates in which the arc plates are attached and retained.